Caesar Cipher and ROT13

Encode and decode Caesar cipher and ROT13 text with any shift from 0 to 25 — free online.

About

About the Caesar Cipher and ROT13

Encodes or decodes text with a classic Caesar cipher, shifting every letter by an amount you choose from 0 to 25.

Puzzle setters use it to encode a clue or riddle, while developers use ROT13 to obscure spoilers or answers in forum posts. It's one of many free text tools on Toolapt, and like every tool here, it's free to use with no sign-up and no limit on how many times you run it.

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Guide

Using the Caesar Cipher and ROT13

  1. 1

    Step 1

    Type or paste your text into the Input box.

  2. 2

    Step 2

    Set the shift amount from 0 to 25.

  3. 3

    Step 3

    Click Encode to shift letters forward, or Decode to shift them back.

  4. 4

    Step 4

    Click ROT13 for the classic 13-letter shift, then Copy the result or Clear to start over.

  • Encodes and decodes text with any shift amount from 0 to 25
  • One-click ROT13 button for the classic 13-letter shift used in forums and puzzles
  • Leaves numbers, punctuation and spacing untouched, shifting only letters
  • Preserves letter case, so uppercase stays uppercase and lowercase stays lowercase
  • Works entirely in your browser — no installs and no sign-up
  • Free to use, with no limit on how many times you run it
  • Fully responsive, so it works just as well on a phone as on a desktop

Puzzle and riddle setters

Puzzle and riddle setters use the Caesar Cipher for encoding a clue or hidden message for others to decode.

Students learning cryptography

Students learning cryptography use the Caesar Cipher for seeing how a simple substitution cipher works in practice.

Forum and community users

Forum and community users use ROT13 for hiding spoilers or answers in a post until a reader chooses to decode them.

Hobbyist coders

Hobbyist coders use the Caesar Cipher for testing basic encoding/decoding logic before building it into their own project.

Examples

Caesar Cipher and ROT13 examples

3 worked examples

01

A shift of 3

"HELLO" shifted by 3 encodes to "KHOOR" — the original Caesar cipher shift.

02

ROT13

"HELLO" with ROT13 becomes "URYYB" — applying ROT13 again returns "HELLO".

03

Punctuation is untouched

"Hi, Bob!" shifted by 5 becomes "Mn, Gtg!" — letters shift, but the comma and exclamation mark stay put.

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FAQ

Frequently asked questions

Quick answers to common questions about the Caesar Cipher and ROT13.

What does the Caesar Cipher tool do?

It shifts every letter in your text forward or backward by an amount you choose, encoding or decoding a classic Caesar cipher.

Is the Caesar Cipher tool free to use?

Yes. It's free, with no sign-up, no watermark and no limit on how many times you use it.

Is my text safe when I use this tool?

Yes. Your text is processed entirely on your own device — nothing is sent to a server.

What is ROT13?

ROT13 is a Caesar cipher with a shift of exactly 13. Because the alphabet has 26 letters, applying it twice returns the original text, which makes it a popular simple way to obscure spoilers.

Is a Caesar cipher secure for real secrets?

No. It's a simple substitution cipher that's easy to break, even without knowing the shift amount, so it's best used for puzzles and novelty rather than genuine security.

Does the cipher affect numbers and punctuation?

No. Only letters are shifted; numbers, spaces and punctuation are left exactly as they are.

Does the cipher preserve uppercase and lowercase letters?

Yes. An uppercase letter shifts to another uppercase letter, and a lowercase letter shifts to another lowercase letter.

Does this tool have any limitations?

It only shifts standard Latin letters A-Z; it doesn't shift accented letters or non-Latin scripts.

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